1. Field of the Invention
The present invention relates to an optical waveguide combiner or splitter, and more particularly to a compact optical waveguide combiner or splitter comprised of a plurality of different s-bends.
2. Background of the Invention
The telecommunications industry currently uses optical fiber to transmit data between users. Several approaches for sending data via optical fiber include the use of an optical waveguide combiner or splitter. An optical waveguide is a material medium that confines and guides a propagating electromagnetic wave such as light. Examples of a waveguide include an optical fiber or a planar lightwave circuit (PLC). A typical optical fiber may be 125 microns in diameter. When used in the communications industry, optical fiber is used as a transmission line that includes an inner dielectric material surrounded by an outer dielectric material. Examples of the outer dielectric material include air, glass, plastic or any dielectric material having a lower refractive index than the inner dielectric material. Electromagnetic waves are guided by a refractive index difference between inner and outer dielectric material so that the waves are confirmed to the waveguide. The waves are confined by refraction or reflection from the outer surface of the guide, or from surfaces within the guide. A waveguide combiner typically takes multiple waveguides or optical fibers and merges them, typically in two or more stages, into an output waveguide, e.g. a single optical fiber, by using S-bends and Y-junctions. A typical splitter reverses the above process by splitting a single waveguide into multiple waveguides.
For a given dielectric waveguide process (i.e., cladding index, core index, core dimensions, functional form of the S-bend), the horizontal size of the device can only be made so small before the losses become unacceptable, i.e., when the radius of the bends becomes to small, a fraction of the power that is guided by the core is radiated out of the waveguide and lost. It is known that the size of the core can be changed or the index difference between the core and the cladding can be increased to allow smaller bend radii.
The geometry of a waveguide process may be modified to make an optical splitter/combiner shorter, while still maintaining acceptable low losses. The Y-branches of a combiner may be modified such that the outputs are tilted. Therefore, full S-bends are not a necessary component of input segments thereof. It is desirable to avoid full S-bends because full S-bends result in extra length of the optical splitter/combiner. The optical splitter/combiner of an embodiment of the invention has a split, i.e., input/output, end that has at least a first input/output segment, a second input/output segment, a third input/output segment, and a fourth input/output segment. The optical splitter/combiner has an upper first stage junction that joins the first input/output segment and the second input/output segment. The first input/output segment and the second input/output segment define an upper first stage bisector. A lower first stage junction joins the third input/output segment and the fourth input/output segment and defines a lower first stage bisector. The third input/output segment and the fourth input/output segment define a lower first stage bisector. An upper intermediate segment communicates with the upper first stage junction. A lower intermediate segment communicates with the lower first stage junction. A second stage junction joins the upper intermediate segment and the lower intermediate segment to form a single input output segment. The upper intermediate segment and the lower intermediate segment define a second stage bisector. The upper first stage bisector and the lower first stage bisector are angularly offset from the second stage bisector. The use of angularly offset bisectors results in a reduced length of the optical splitter/combiner.